GPS World, August 2013

EXPERT ADVICE Vapor Cell Glass Blown Coils VCSEL Wafer Level Optics Polyimide Hinge FIGURE 1 C SCAN conceptual implementation The deliverable is a miniature IMU that co integrates atomic and solid state inertial sensors in a single microsystem with a volume of no more than 20 cubic centimeters 20 cc and power consumption of no more than 1 Watt 1 W The performance of C SCAN is expected to be above and beyond what is currently available combining a high resolution of motion detection 10 4 deg hour for rotation and 10 6 g for linear acceleration exceptional long term bias and scale factor stability 1 ppm with respect to the full scale of operation and start up time performance orders of magnitude better than available today less than 10 seconds from cold start To meet these objectives the C SCAN program expects to develop a complete IMU comprised of combinatorial gyroscopes and accelerometers with the following characteristics 10 4 deg hour and 10 6 g bias stability 5 10 4 GHJ KRXU DQJOH random walk ARW and 5 10 4 m VHF KRXU 9HORFLW 5DQGRP DON 95 SSP ELDV DQG VFDOH IDFWRU drift characteristics of 40 Hz or 15000 deg sec and 1000 g range of operation respectively The C SCAN module will have three axes of rotation as well as three axes of acceleration sensitivity The misalignment between the axes of sensitivity in C SCAN is not to exceed 10 4 radians when operating in a harsh military environment The operational environments of interest are in operation exposure to Via Integrated Heater Latch SOI sensors Vacuum Lid Interconnects Hinge Flex Bus temperatures varying from 55 º C to 85 º C in operation exposure to mechanical vibrations from 5 Hz to 5 kHz with an average amplitude 5 g and device survivability and subsequent normal operation after exposure to 15000 g shock exerted in less than 1 second a peak acceleration amplitude on the level of 20 g through the frequency range for random vibrations from 5 Hz to 5 kHz and a 100 º C temperature difference thermal shock with transfer time not exceeding 10 seconds Current state of the art microscale inertial instruments can provide the required level of precision for missions of only 30 seconds or less in duration The micro PNT program is developing chip scale small SWaP C Size Weight and Power plus Cost inertial sensors for a variety of operational scenarios missions ranging from minutes to hours and for reliable operation under environmental conditions varying from moderate to severe Ongoing work includes development of a broad range of chip scale precision timing devices and inertial sensors including chip scale atomic clocks chip scale primary atomic clocks solid state oscillators silicon accelerometers and various gyroscopes vibratory rate rate integrating electrostatically levitated spinning mass micro nuclear magnetic resonance and cold atom interferometric While recent results in the micro PNT program have shown considerable progress toward development of smallscale inertial instruments approaching navigation grade performance the overall challenge remains how to simultaneously meet all the stringent PNT requirements imposed by U S Department of Defense missions in a small SWaP C package Specific requirements include but are not limited to accuracy resolution scalefactor bias stability both in run and long term extended dynamic range fast warm up time and short integration time These challenges are significant and it is unlikely that all the requirements can be achieved in a single type of device Overall more than 98 percent of the missiles currently in the U S arsenal have mission durations of less than 20 minutes and today almost all of these missions are critically dependent on GPS for achieving the required level of delivery accuracy A preferable solution is to completely eliminate dependence on GPS or any other external signals during the mission and rely solely on self contained solutions such as inertial navigation which is immune to jamming spoofing and other intentional or unintentional modification of position orientation and time information Achieving 20 minutes of free inertial guidance is a major technological challenge faced by small SWaP C inertial instruments Solving this problem is of great strategic importance Several recent developments in micro technology inertial instruments and atomic devices may present an opportunity for solving the problem of extended inertial guidance and navigation potentially offering a new breed of chip scale navigators exhibiting favorable characteristics when combined in a single hybrid micro system ensemble ANDREI M SHKEL received a Ph D in mechanical engineering from the University of Wisconsin Madison and is a program manager in the Microsystems Technology Office at the Defense Advanced Research Project Agency DARPA GPS World August 2013 www gpsworld com 10

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